Internal combustion piston engines include a piston connected to a crankshaft, where the piston is made to move in a cylinder by the timed expansion of gases in the cylinder. Two or more valves are provided for the cylinder to allow the intake and exhaust of gases, where these valves are opened and closed for appropriate times and durations to achieve the desired engine performance. For example, piston engines can use valves for intake and exhaust which are driven by rotating cams on a camshaft. The cams open the valves (lift) for a certain amount of time (duration) during each intake and exhaust cycle. The timing of the valve opening and closing is also important. The camshaft can be driven by the crankshaft through timing belts, gears or chains.
Swirl or tumble is the rotational flow of induced air inside the combustion cylinder of the engine which enhances the mixing of fuel and air and combustion products. The swirl can be generated, for example, by providing an intake port in a cylinder head in the tangential direction with respect to the corresponding cylinder to cause swirl in the cylinder, or by providing a shape of intake port that induces swirl in the port, such as a helical shape. A mixture of fuel can be input into the swirled air and ignited to achieve combustion in the cylinder. Different swirl characteristics can lead to different engine performance, such that different desired operation speeds of the engine may require different swirl characteristics. For example, in different circumstances or physical characteristics, swirl can affect detonation, emissions, fuel efficiency, and/or other engine performance.
Beneficial swirl tends to be a function of engine speed and other operating conditions. Thus, it is often desirable to have a controllable variable swirl in engine cylinders to tune the performance of the engine. For example, high speed diesel engines can benefit from having variable swirl ratios that depend on engine operating conditions.
Swirl can be controlled using the intake valves to the cylinders. Engines having two intake valves and two exhaust valves per cylinder can generate swirl by controlling the flow rate to one of the intake valves differently than to the other. The flow through one port can be changed, which tends to change the swirl in the cylinder. In previous designs, a separate solenoid and appropriate electronics, extra butterfly valve, or other mechanism, is provided in one of the intake ports and is used to reduce or modulate air flow through that port based on engine speed or other criteria, thus modifying the swirl based on those criteria. However, such additional required electronics and mechanisms add to the expense of manufacturing an engine.
Accordingly, a system and method for providing variable swirl at different engine speeds with reduced expense would be desirable in many applications.